FIG. 1 is an example of a prior art two-stroke motor reed valve. Reed valve 10 includes a V-shaped base 12, pliable reed petals 14, and stoppers 16. Base 12 is substantially hollow with a plurality of openings (shown with a dotted line) covered by reed petals 14. In operation, air flows into the center of base 12 and through the openings in base 12, pushing reed petals 14 back towards stoppers 16. When the air reverses flow, reed petals 14 press firmly against base 12, covering the openings and substantially impeding airflow through base 12. Reed valves are typically located between an air induction control device, such as a carburetor or a throttle body, and an opening into the crankcase of an engine. However, a common variant of the two-stroke engine has the reed opening in the base of the cylinder instead of in the crankcase.
A limitation with this prior art design is only a limited amount of airflow enters the engine within the space constraints of a typical two row reed valve. As discussed above, traditional two row reed valves have one row of reeds on each side. These reeds only open a certain distance, which is dictated by the differential pressure across the reeds. That is, the differential pressure can only open the reeds to a certain deflection due to resistance of the reeds to stay in a closed position. This provides a limitation to the amount of airflow, which can realistically pass through the reed valve.
Prior reed valve designs have tried to overcome this limitation by adding a second row of reed valves, so that there are four rows of reeds instead of two. FIG. 2 is an image of a prior art four row reed valve assembly similar to those described in U.S. Pat. Publication 2003/0209275 to Tassinari and Japanese Abstract 03-061610A2 to Yoshinori. Reed valve 20 includes a W-shaped base assembly 22, pliable reed petals 24, guards 26, and an inner stopper 28. The design of this reed valve 20 creates a broader opening for allowing passage of air and improved engine performance. Also reed petals 24 against guards 26 do not have to bend as far as reed petals 14 in a traditional reed valve 10 for reed valve 20 to allow more airflow than the traditional reed valve 10 because of the additional volume of airflow allowed past the reed petals 24 against the inner stopper 28. However, these prior art designs are still limited in the amount of volume of airflow allowed past the reed petals due to the length of time the petals are actually open. This is due to the fact that as a reed petal opens towards a stopper there will be air trapped between the stopper and the reed petal. This prevents the reed petal from fully opening until the air is pushed out from behind the petal. The longer the reed petal is not fully opened, the greater the volume of air passing the reed petal is decreased. This is undesirable and limits engine performance.
Another limitation associated with the four-row reed valve design is they are a multi-piece assembly, which requires assembly. For example, these prior art designs typically have a muti-part cage design along with all the other pieces of the assembly. Due to the number of pieces of the assembly and the amount of labor required to assemble, the assembly becomes expensive to produce especially for mass production.
Another limitation with the traditional 2-stroke motor reed valves is durability. A reed petal 14 opens and closes about 133 times per second at 8,000 rpm. The fatigue on the reed petals 14 requires regular replacement of reed petals 14. Further, in a four-row reed design like that of FIG. 2 without a stopper, the inner reeds can be damaged by hitting each other when they open. Prior reed valve designs have attempted to solve this problem by inserting an inner stopper between the inner petals to prevent the inner petals from hitting one another. Typically, these inner stoppers have some arbitrary curved shape to keep the reeds from hitting each other. While these stoppers have been successful at stopping the inner reeds from hitting one another, the reeds do continue to hit the inner stopper, as designed. Since the inner stoppers have an arbitrary curved design, reed petals continue to fail due to the reed petals hitting against the inner stopper in an arbitrary fashion. The arbitrary shape of the stopper also forces the reed to deform to the shape of the stopper rather than its natural shape. This also limits airflow by restricting reed deformation. Therefore a reed valve assembly design is needed that reduces wear on the reed petals.